The present invention relates in general to drive systems for electric vehicles, and, more specifically, to the rapid discharging of capacitors when shutting down the electric drive system.
Electric vehicles, such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), use inverter-driven electric machines to provide traction torque and regenerative braking torque. The inverter module (i.e., the inverter system controller, or ISC) typically employs a relatively large energy storage capacitor as a main DC link to maintain a desired bus voltage and absorb switching related ripples. The DC link capacitor is usually interfaced with a high-voltage (HV) battery through a pair of mechanical contactors.
A shutdown of the electric drive system can be initiated by various events. During such a shutdown, the HV battery is quickly isolated from the rest of the electric system by opening the mechanical contractors. However, a HV electric charge will remain on the DC link capacitor. Due to safety requirements, the HV electric charge should be quickly discharged within a specific time. For example, U.S. Federal Motor Vehicle Safety Standards (FMVSS) may require that the voltage on the DC link capacitor must be less than 60V within 5 seconds in certain circumstances.